64 Moderate body weight loss and one-carbon metabolite supplementation in early gestation beef heifers alters the fetal liver transcriptome.

Abstract Moderate body weight (BW) loss occurs in production cycles, particularly among heifers with increased nutrient demand from pregnancy, ultimately hindering fetal growth and development. Feed costs and associated labor create a challenge for providing supplemental feed. However, stimulating the one-carbon metabolite cycle may alleviate this problem. The objective of this study was to determine if moderate changes in rate of BW gain and one-carbon metabolite (OCM) supplementation in early gestation beef heifers alters fetal liver gene expression. Angus-cross heifers (n = 72) underwent estrus synchronization and were bred to a single sire using female-sexed semen. At breeding, heifers were stratified by BW into a 2 × 2 factorial of treatments: fed to gain 0.45 kg/d (CON) or lose 0.23 kg/d (RES) BW and to receive corn carrier with OCM supplements (+OCM) or without (−OCM) from d 0 to 63 of gestation. The OCM supplements consisted of vitamin B12 (20 mg/wk) and folate (320 mg/wk) injections and dietary rumen-protected methionine (7.4 g/d) and choline (44.4 g/d). On d 35 of gestation, pregnancy diagnosis confirmation was performed using transrectal ultrasonography. The heifers confirmed pregnant with female fetuses across treatments were CON−OCM (n = 7), CON+OCM (n = 7), RES−OCM (n = 9), RES+OCM (n = 8). On d 63 of gestation, heifers were slaughtered and the fetus was excised and dissected for fetal liver collection. Total RNA was extracted and subjected to quality control, then sequenced on the Illumina NovaSeq 6000 platform. Reads were mapped to the ARS-UCD1.2 reference genome using STAR, then differential gene expression was analyzed using DESeq2 (log2fold ≥ |1| and P ≤ 0.05). KEGG pathway enrichment was conducted using ShinyGO at nGenes ≥ 2 and FDR ≤ 0.10. There were 114 differentially expressed genes (DEG) in RES+OCM vs. CON−OCM. HTRA4 is involved in apoptosis and programmed cell death, and was upregulated > 2.5-fold in RES+OCM. Whereas, ADCYAP1R1, a gene involved in regulating stress responses, was downregulated > 6-fold in RES+OCM. There were 108 DEG in RES−OCM vs. CON+OCM, and the GnRH secretion pathway was enriched. No other pathways were enriched among other contrasts. PRSS56, a negative regulator of MYRF, was downregulated > 3.5-fold in RES−OCM. There were 78 DEG in RES+OCM vs. CON+OCM. There were 155 DEG in RES−OCM vs. CON−OCM. PRSS56 was downregulated 2.9-fold in RES−OCM. There were 108 DEG in CON+OCM vs. CON−OCM. SOX8, a gene involved in organogenesis was upregulated 3-fold in CON+OCM, while ADCYAP1R1 was downregulated > 6-fold. There were 113 DEG in RES+OCM vs. RES−OCM. Taken together, moderate BW loss and one-carbon metabolite supplementation during early gestation altered fetal liver gene expression. Most notably, ADCYAP1R1 was down regulated in response to OCM supplementation in both CON and RES groups.

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